Revert "fmt: check newline in the end of input"

Revert "fmt: check newline in the end of input"

This change can break real code. There are other newline-related bugs in this code, and fixing them will also break real code. If we're going to break real code, let's fix all the bugs together and just break things once.

This reverts commit 8331f19d9700457d74bf377755ca270a32d2faa3.

Change-Id: Ie4b3022f3a305c3e1f78cc208e50beed212608e6
Reviewed-on: https://go-review.googlesource.com/17724
Reviewed-by: Rob Pike <r@golang.org>